capture and expose the last download date of an asset

Capture and expose an asset last downloaded date in the asset detail view. Expose this piece of metadata as a common asset property and make it accessible for searching and as metadata for tasks and viewing.

Use cases:

• tasks which want to operate on components by the date they were last downloaded
• searching by last download date or date span for assets
• viewing informationally metadata about a particular asset for any variety of knowledge gathering requirements

Criteria

• the date should be updated if a download is started. Finishing the download is not required
• for requests for an asset which initially return a 401, the download date should NOT be updated because the download did not technically start ( requires an authenticated request)
• a download date may be through a group repo or to the source repo directly, in either case update the last download date
• a download attempt == a download for the purposes of updating the date